The leaks can lead to massive and costly water main breaks. Water customers pay to treat water at facilities along Lake Michigan through their bills and taxes. One national estimate puts the cost of lost, treated water due to leaks across the country at $2.8 billion dollars a year.

"A lot of the infrastructure that was put in the turn of the last century and infrastructure that was put in post-World War II is coming to the end of its useful life," said the CNT's Danielle Gallet.

In fact, a city spokesperson said of the 4,300 miles of water mains under the city, about a quarter of them are more than 100 years old.

However, the utility said it is taking a proactive stance against the leaks. "We check about a thousand miles of water main every single year looking for leaks before they become catastrophic," said commissioner Thomas Powers.

Crews are also upgrading the city's water infrastructure. Workers have installed more than 145 miles of water pipes in the past two years.

The upgrades are part of the Mayor Rahm Emanuel's Building a New Chicago program.

"We raised water rates to tackle and to replace these water mains," Powers said.

While the CNT said the city's water main upgrades and inspections are good, they may not be enough. The group is calling for a national standard for reducing water loss.

The CNT is urging utilities to perform water loss audits, which it said could pinpoint spots known for leaks.

"It would be wonderful to see water utilities, every single one of them, doing a robust water loss audit every year," Gallet said.

But the audits may not be possible in Chicago.

Many area water customers do not have water meters. In those cases, the utility said there is no way to find out how much water gets lost.

Still, the city urges its water customers to sign up for water meters. The Department of Water Management said in recent years it has seen a 20 percent decrease in the amount of water coming out of its water treatment plants, thanks in part to its customers who have the meters.